This invention pertains in general to current monitors and more particularly to such circuits that monitor either AC or DC over a wide continuous range of magnitudes.
It is often desirable to monitor the current through a load energized by a source supplying current over a range of several orders of magnitude. Several such circuits have been devised by the prior art for this purpose, such as the circuit arrangements illustrated in the patents to: Brooks, U.S. Pat. No. 3,665,442, issued May 23, 1972; Vinsani et al, U.S. Pat. No. 3,662,369, issued May 9, 1972; A. R. Morris, U.S. Pat. No. 3,505,664, issued Apr. 7, 1970; R. E. Monigal et al, U.S. Pat. No. 3,548,399, issued Dec. 15, 1970; and the patent to E. H. Christian et al, U.S. Pat. No. 3,021,515. The current monitoring ranges and versatility of these circuit arrangements are often limited by the circuit components provided. For example, the range provided in the patent to Brooks is limited by the characteristics of the field effect diode employed.
In addition, an inexpensive, reliable, monitoring circuit is desired with the capability of indicating the continuity of DC current in a circuit without the necessity of reorganizing the circuit components. Many of the prior art devices require rearrangement of their corresponding components for this purpose, or the addition of new components which escalates the expense of employing such units.
The problem of circuit monitoring becomes even more acute when it is desired to test the operation of a switch in series with an energized load whose operation cannot be interrupted. No simple, inexpensive, reliable, on-line circuit arrangement appears to be presently available for this purpose. Accordingly, a new current monitor is desired having the versatility of satisfying the aforedescribed characteristics.